High energy density and rapid charge/discharge capabilities of lithium ion batteries makes them ideal candidates for use in portable electronic devices such as cell phones, MP3 players and laptop computers. Recently, larger size lithium ion batteries have been developed and have applications for use in the hybrid vehicle (HEV) and the plug-in hybrid electric vehicle (PHEV) markets.
Lithium batteries typically comprise of a pair of electrodes and an electrolyte solution filled between them. An electrolyte solution with lithium salts dissolved in an aprotic solvent is an indispensable component in lithium battery chemistry. The availability of lithium salts for electrolyte applications is rather limited when compared to the wide spectrum of aprotic organic compounds that are available for use as electrolyte solvents. Many of such lithium salts are based on complex anions that are composed of a single anion core stabilized by a Lewis acid agent. For example, the anion of lithium hexafluorophosphate (LiPF6) could be viewed as F-complexed with the Lewis acid PF5.
Overcharge protection for lithium ion batteries has been proposed by imparting various chemical moieties, which are designated as “redox shuttles” or “shuttles.” In theory, the redox shuttle can provide an oxidizable and reducible charge-transporting species that may repeatedly transport charge between the negative and positive electrodes once the charging potential reaches higher than the working potential of the positive electrode of lithium-ion batteries. If the battery is overcharged, the battery voltage will reach the redox potential of the redox shuttle first and then activate the redox mechanism, which will proceed as the only active component to transfer the excessive charge through the battery without causing damage to the positive active material. Under such a mechanism, adverse events caused by overcharge abuse of a battery, such as battery explosion, can be mitigated or even eliminated.
Lithium batteries typically comprise of a pair of electrodes and an electrolyte solution filled between them. The electrolyte solution contains a salt as an electrolyte, which is dissolved in a non-aqueous solvent such that the salt is dissociated into cations and anions, which supportionic conduction. Electrolytes having sufficient solubility in organic solvents are presently limited to a handful of electrolyte salts, for example, LiClO4, LiPF6, LiBF4, Li[B(C2O4)2] (LiBOB), Li[BF2(C2O4)] (LiDfOB), LiAsF6, LiN(SO2CF3)2, LiN(SO2(C2F5))2, LiN(SO2CF3)(SO2C4F9), and Li[SO3CF3]. All the above salts provide a single functionality, i.e. that of an ion source for the electrolytes.